Conductor



April 29, `1930. J, F, WENTZ 1,756,319

CONDUCTOR Filed March EJI 1925 Patented Apr. 29, 1,930

:UNITED STATES PATENT? OFFICE JESSE IF. WENTZ, OF NEW YORK, N. Y., ASSIGNOR, BY MESNE ASSIGNMENTS, TO WESTERN ELECTRIC COMPANY, INCORPORATED, A CORPORATION OF NEW YORK connuc'ron Application filed March 9, 1925. Serial No. 13,(943.I

' of alternating current is to wrap the conductor spirally with a layer vof wire or tape of magnetic material. This method is known in the art as continuous inductive loading as distinguished from lum loading by means of inductance coils distri uted at intervals along the conductor. Until recently iron has been considered to be the only material suitable for continuous loading but it has now been discovered that a more suitable material may be procured in the form of an alloy of nickel and iron. When these two metals are combined in the proper proportions and the resulting alloy is given'a proper heat treatment, a material having a very high permeability at'low ma etizing forces is obtained.

ne form of thismaterial which hasbeen used in a submarine cable comprises 781/270 nickel and 2l1/2% iron. Alloys of nickel and iron having similar characteristics, especially high ermeability at low magnetizing forces, have Ibeen styled permalloy. Other properties possessed by these alloys which increase their value as a loadin material are a hysteresis loss lower than tlat of iron anda high resistivity, both properties being conductive to increasin the eiciency of the cable by lowering the e ective resistance of the conductor.

When it was attempted to employ this materia-lin the form of a tape for continuous loading, difficulties were encountered. It was found thatV if the pe'rmalloy tape Was first heated and then cooled before applying to the conductor, internal stresses were set up upon bending of the tape, causing the permeability to be very materially lowered. This difficulty was overcome by ,applying the tape to the conductor before giving the tape the heat treatment and then subjecting the taped conductor to the -heating and cooling necessary to pro- -duce high permeability in the loading material.

Further difficulty, however, Was experimaterial was lowered by what appeared to be adhesion between the copper conductor and the loading tape. It is believed that this adhesion occurs when the taped conductor is subj ected to the high temperatures necessary for the proper heat treatment and that upon subsequent cooling the tape is subjected to stresses which cause a lowering of its permeability.

In the construction of a loaded conductor it Was the practice to wrap a layer of magnetic material comprising a nickel-iron alloy closely around the conductor consisting of a central copper wire surrounded by six flat copper ture with very little space not occupied by metal. To give the loading material the desired magnetic characteristics, this conductor was heated to approximately 850 C. and then cooled at a preferred rate. On heating, both metals expand but the copper, because of its higher temperature coefficient, expands more than the loading material with the result that it presses tightly against the loading material when the conductor is at the high temperature and if thel structure is a fairly tight one, the magnetic tape is stretched, an elongation of as much as 1% having been observed. This stretching however, has apparently no direct e'ect on the magnetic properties since it occurs at a temperature above the magnetic transformation point but it does show effects of high pressure between the metals. At the' temperature of 850 C. both metals are relatively soft and since they are forced together by thermal expansion there is a tendency for the loading material to weld to the copper, the'extent to which the metals are ywelded depending on several factors such as the tightness of the copper structure and the character of the metal surfaces. In this connection it has been noted that although the -loading material welds to the copper, welding of the copper strands to the central wire has been Very rarely observed and no welding has been observed between layers of the loading material when more than one layer has been used. These results suggest that welding is possibly not a simple caseof fusion of the two metals 100 but some effect brought about by chemical action.

On cooling, the. copper conductor contracts more than the magnetic tape. No doubt some of the welds which have been formed break loose when this contraction occurs butthe stronger ones hold with the result that the magnetic tape is at points pulled down with the copper and parts of it are bent, stretched or compressed depending upon the particular accidental conditions of adherence. Even though the forces involved may be very small, the stresses at points in the tape may be of considerable magnitude giving strain sufficient to reduce the permeability at spots to a very smallfraction of that which the tape would have had if not subjected to such strain. The resultant conductor, therefore, is one which although it may have fairly uniform inductance as measured from foot to foot is loaded with a material which varies in permeability over a wide range in points separated by a fraction of an inch.

The. copper vtapes upon being stranded about the centrall conductor do not present a true cylindrical surface Since the edges of the strands do not lies in close contact with the central conductor but present spiralled edges. As the cooling proceeds, therefore a sticking or welding of the material `may occur at various points along these edges and.

the subsequent contraction ofthe copper set up stresses in the alloy tape.

During the Cooling portion of the heat treatment the alloy tape may cool more rapidly at first than does the copper conductor due to its intimate Contact withthe cooling medium so that the alloy tape quickly comes into intimate contact with the copper strands.

Whatever may be the true explanation for the difficulty experienced, it has largely been overcome by providing a small air space between the layer of loading material and the signaling conductor when the loading material is applied. This method of obtaining high permeability is described at length in patent to G. W. Elmen, No. 1,586,887 granted June 1, 1926.

Instead of providing an air space between the conductor and the tape, as the latter is wound in position, the desired result may be obtained by placing a layer of paper upon the conductor before the loading material is wound thereon. This layer of paper is burned out during the subsequent heat treatment thus giving the desired spacing'between the loading material and the conductor. This method is described in detail in patent to W. B.` Ten Eyck, No. 1,586,862, granted June 1, 1926. An object of the present invention is to provide for the practical loading of a signaling conductor with a magnetic material which requires heat treatment and whose characteristics are subject to undesired change under applied stresses.

Another object of the invention is to provide a method of applying magnetic loading material to an electrical conductor in such a manner as to prevent the setting up of deleterious stresses in the magnetic material during the subsequent heat treatment.

To accompllsh these objects, the inventlon contemplates an electrical conductor, upon which is applied loading material capable of possessing high permeability, and the method of applying this material to the conductor in such a way as to avoid obtaining low or variable values of permeability. This invention is in the nature of an alternative to that disclosed in a copending application of O. E. Buckley, Serial No. 758,984, filed December 31, 1924, and to the above mentioned patents of G. W. Elmen and W. B. Ten Eyck. Each of these inventions has certain advantages over the others, as will be apparent from a consideration of the application and patents mentioned above.

The invention may be more clearly understood by reference to the accompanying drawing, in which Fig. 1 is a view of a loaded conductor embodying the features of the invention, certain portions of the conductor being shown cut away to more clearly disclose the structure; and Fig. 2 is a view showing a simple type of apparatus which may be used for applying the heat treatment to the conductor.

Referring to the drawing, the electrical conductor preferably comprises a central core 10 of copper or similar conducting material about which a plurality of' conducting strands 11-11 are wrapped with a spiral lay in such a manner as to provide a smooth exterior surface. The exterior of this conductor as at 13 is roughened by rubbing with an abrasive, such as sandpaper, or by subjecting it to the action of a sand blast. About the roughened surface 13 is closely wrapped the magnetic loading tape 12 which preferably consists of an alloy containing 781/270 nickel and 211/2% iron.

After the composite conductor is provided with one or more layers of magnetic tape applied suiiiciently tightly to make a good mechanical structure, the resulting conductor is treated by passing it through a heated tubular furnace of the type disclosed in Fig. 2. v This furnace which is of the muiiled tylpe comprises heating elements 304which are ocatedbetween the fire-clay muie 31 and the fire brick- 32. The iron tube 33 has ,a copper lining 34 of lsuch small inside diameter as to plrevent rapid circulation of air which mig t cause an objectionablede ee of oxidization of the magnetic tape.

or the sake of clearness, this apparatus has been shown issued as Patent No. 1,624,668 on April1i2,

but reference is made tofan 1927 and which discloses the preferred form of apparatus to be used.

By providing an imperfect Contact between the central conductor Vand the loading tape as is done by roughening one of the surfaces, the trouble due to adhesion formerly experienced has been largely overcome resulting in an improved conductor because of the higher permeability of the loading material. Itis believed that this improved result is due to the fact that when the surfaces are roughened, the points of contact between the conductor and tape Vare of very small area; and although Welding takes place at these points, these Welds are readily broken up on contraction of the copper conductor Without impressing undue strains on the magnetic tape. It is further possible that the cleanving of the conductor surfaces and the consequent removal of sulphides and other materials from the surface are partly instrumental. in reducing the adhesion between the loading material and the conductor. Although it is preferable to roughen the surface of the conducting member because of its mechanical nature, an imperfect contact can also be obtained by roughening the under-surface of the tape.

lWhat is claimed is:

1. A loaded signaling conductor comprising a central conductor having a rough, eX-

terior surface, and a magnetic loading material Wrapped closely about the rough surface, said loading material requiring heat treatment to develop high permeability therein, and thel permeability of which is sensitive to strain, said rough exterior surface vcontacting with said loading 'material at a., large number of closely spaced areas, thereby preventing the loading material from Welding securely to saidsurface during the heat treatment.

2. A loaded signaling conductor comprising a central conductor having a cylindrical exterior surface roughened as by an abrasive, and a magnetic loading material Wrapped closely about the rough surface, 'said loading material requiring heat treatment to develop high permeability, therein, and the permeability of which is sensitive to strain.`

3. 'A loaded signaling conductor comprising a central conductor having la cylindrical exterior surface roughened as by an abrasive, and a magnetic loading material Wrapped clo'sely about the roughened conductor, said loading material comprising a nickel iron alloy in Which the nickel component predominates. t

4. A loaded signaling conductor comprising a central conductor-having a cylindrical exterior surface roughened as by an abrasive, and a magnetic loading material wrapped closely about the roughened conductomfsaid loadingk material containing 781% nickel and 211/% iron.

5. In a methodfof constructing a continuously loaded conductor having a` cylindrical conducting portion and a magnetizable portion formmg a layer Wrapped in close contact with said conducting portion and which requires heat treatment to improve one of its electrical characteristics, the step of roughening the -contactinff surface of one of said portions to reduce deleterious interaction between said portions during said heat treatment.

6. The method of constructing a continuously loaded conductor which comprises roughening the surface of the conducting member by rubbing With an abrasive, Wrapping a layer of magnetic material closely aboutthe conducting member, and heat treating the loaded conductor'.

7. A loaded signaling conductor comprising a conducting member having an outer surface and a magnetic member Wrapped thereabout having an inner surface in .close contact With said outer surface, one of said surfaces being roughened to form a large number of sharp closely spaced areas of contacts with the other of said surfaces thereby preventing the magnetic member from Welding to said outer surface.

8. A loaded signaling conductor comprising a central conducting member and a magnetic loading material Wrapped in close contact with said conducting member, said conducting member having a lcontinuously interrupted outer surface for supporting said loading material by a large number of sharp, closely spaced contacts, thereby preventing the loading material from Welding securely to said surface during the heat treatment.

9. A loaded signaling conductor comprising a central conducting member, a magnetic loading material wrapped in close contact with said conducting member, and means in- `tegral with the surface of one of the contacting elements for preventing the conducting member and loading material from securely Weld-ing to each other' during heat treatment of the loaded conductor.

10. A loaded signaling conductor as de 'scribed in claim 9 in which saidmeans com- 

